Operating a motorboat under the influence is a crime in Montana, but it is not a DUI. It is a separate misdemeanor in the boating code, MCA § 23-2-523(2), with a lighter penalty range and different testing rules. This page explains who the law covers, how it is proved, and how it differs from a DUI on the road. It is part of our Montana DUI Guide and goes further than our overview of DUI on a horse, bike, ATV, or boat.
What the Statute Prohibits
The text is one sentence: "A person may not operate a motorboat, including a sailboat propelled by a motor of any kind, or manipulate waterskis, a surfboard, or a similar device attached to a motorboat while under the influence of alcohol, drugs, or a combination of the two" (MCA § 23-2-523(2)).
Three definitions fill it in:
- Motorboat means a vessel "propelled by any machinery, motor, or engine of any description, whether or not the machinery, motor, or engine is the principal source of propulsion." It includes a personal watercraft, a pontoon, and boats temporarily equipped with detachable motors (MCA § 61-1-101). A drift boat or raft fitted with a kicker motor can be a motorboat.
- Operate means "to navigate or otherwise use a motorboat or a vessel" (MCA § 23-2-502(8)).
- Under the influence has the same meaning as in the DUI laws: a person's ability to safely operate has been diminished (MCA §§ 23-2-535(5), 61-1-101).
Notice who else is covered. The person on the skis, wakeboard, or tube behind the boat is within the statute, not only the person at the wheel.
BUI Compared With DUI
| Point | DUI on the road | Boating under the influence |
|---|---|---|
| Statute | MCA § 61-8-1002 | MCA § 23-2-523(2) |
| What you must be operating | A vehicle | A motorboat, a sailboat propelled by a motor, or waterskis, a surfboard, or a similar device attached to a motorboat |
| Meaning of under the influence | Ability to safely operate has been diminished (§ 61-1-101) | The same definition (§ 23-2-535(5)) |
| A 0.08 result | A separate per se offense, and an inference of impairment | An inference of impairment that can be rebutted; no separate per se offense in the boating statute |
| Penalty | Set by § 61-8-1007, with mandatory minimums | Fine of $15 to $500, up to 6 months in jail, or both (§ 23-2-507(1)) |
| Refusing a test | License suspension under the implied consent law | No test is given; the refusal is admissible; no suspension is stated (§ 23-2-535(3)) |
How Impairment Is Proved on the Water
Because the boating statute has no per se subsection, the State has to prove the operator was actually under the influence. A test result helps the State through the inferences borrowed from the DUI statute (MCA § 23-2-535(1)), and the 0.08 inference is rebuttable. Evidence of any measured amount of alcohol or drugs in blood, breath, oral fluid, or urine is admissible, along with "any other competent evidence" on the question (MCA § 23-2-535(2)). The technical rules for administering tests in DUI cases apply to boating tests too (MCA § 23-2-535(4)).
The rest of the evidence is observation: how the boat was handled, how the operator looked and spoke, and how any coordination tests went. Where and how those tests were given matters. A test given on a moving deck or a floating dock is a different thing from one given on a level roadside, and a defense lawyer will ask about the conditions. Our page on field sobriety tests explains what the standardized tests are and how they are supposed to be administered.
Refusing a Test
If a person charged with boating under the influence refuses a test of blood, breath, or urine, "none will be given, but proof of refusal is admissible" in the criminal case (MCA § 23-2-535(3)). The boating statute does not state a license suspension for that refusal.
That is a real difference from the road. Montana's implied consent law, with its administrative suspension, applies to a person operating "a vehicle or commercial motor vehicle upon the ways of this state open to the public" (MCA § 61-8-1016(1)(a)). Our page on refusing a DUI test covers those consequences. Do not assume the two situations stay separate, though: a person who drives the truck and trailer away from the ramp is back under the DUI statute.
The Penalty
A violation of the boating part is a misdemeanor punishable by a fine of not less than $15 or more than $500, imprisonment for up to 6 months, or both (MCA § 23-2-507(1)). The boating section does not set a mandatory minimum jail term or a different penalty for a repeat offense. A boating conviction is still a criminal conviction, and it can matter for employment, professional licensing, and any later sentencing.
More serious charges are possible if someone is hurt. Which statute applies to an injury or death on the water depends on the facts, and that is a conversation to have with a lawyer early.
Reckless or Negligent Operation Is a Separate Offense
Subsection (1) of the same statute prohibits operating a motorboat or vessel, or manipulating skis or a similar device, in a reckless or negligent manner that endangers life, limb, or property. It gives examples such as weaving through congested traffic and jumping a wake unreasonably close to another vessel. This subsection applies to any vessel, and an owner who knowingly permits that kind of operation is covered as well. Officers sometimes cite it along with, or instead of, the under-the-influence subsection.
National Park Waters
On waters inside a national park area, such as the lakes of Glacier National Park, a federal regulation applies. It prohibits operating or being in actual physical control of a vessel while under the influence to a degree that makes the operator incapable of safe operation, or with an alcohol concentration of 0.08 or more (36 CFR § 3.10). An operator must submit to testing on a ranger's request based on probable cause, and refusal "is prohibited" (36 CFR § 3.11). Those cases go to federal court. See DUI in national parks.
This page explains Montana and federal law in general as of October 2026. It is not legal advice about your specific case.